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8 Steps to Mixing Concrete by Hand

8 Steps to Mixing Concrete by Hand

Make Concrete Without a Mixer

A cement mixer does a great job at mixing concrete, thoroughly blending cement, stone and sand to give a consistent result. However it's also possible to mix concrete by hand without a mixer with a little care and some effort. Sometimes the need arises to mix concrete for setting gate, fence posts or a clothes line into the ground. Another possibility is that you have to make a concrete slab to act as a base for something like a fuel bunker. All you need for mixing concrete are the three materials, water and minimal tools: A shovel, a couple of buckets and optionally a sheet of plastic.

This is the first of a two part guide. My other guide shows you how to use a cement mixer for making concrete:

How Do I Mix Concrete? - 8 Easy Steps!

  1. Spread a plastic sheet on the ground.
  2. Measure out the materials.
  3. Place the stone and sand into a pile on the sheet.
  4. Place the cement on top of the pile of sand and stone.
  5. Shovel the material in the pile to one side, creating a new pile and repeat three times.
  6. Make a deep crater in the pile and add water.
  7. Fold the mix in from the sides.
  8. Continue to fold inwards and "chop" the pile to distribute water through the mix.

See below for lots more details and photos.

What is Cement?

Cement is a binder, used as an ingredient in combination with sand and stone (types of aggregate) to make a composite material called concrete. The three constituents on their own have no real strength but when bound together, stones interlock like a 3D jigsaw puzzle and sand and cement fills the gaps. Cement just glues the stones and sand together but it's the stone that gives concrete its shear and compressive strength, not the cement.
There are several different types of cement, two examples are Portland cement and blast furnace slag cement. Portland cement is made by baking limestone in kilns and grinding the clinker produced with a little gypsum to form a fine powder. Blast furnace slag cement is made from the waste products of the steel industry.

Your Options - Pre-mix Concrete or Make Your Own

If you need to mix concrete by hand, there are two options:

  • Buy a bag of pre-mixed concrete (drymix). This is available at all good home improvement stores. It has all the ingredients dry mixed together for making concrete, i.e. the cement, sand and stone. All you have to do is put it into a bucket, wheelbarrow or on a piece of plastic on the ground, add water and spend a few minutes mixing it. Usually the product comes in 2 to 4 stone bags ( 10 kg to 25 kg) with varied setting times. Quick setting concrete is available for fixing posts into the ground so that they don't have to be stayed.
  • Premixed products from stores tend to work out more expensive if you're going to need several wheelbarrows of concrete. The alternative is to mix your own. All you need is cement, sand and stone (20 mm). Instead of sand and stone you can use ballast (mixed aggregate or "all in") which is a mixture containing varying sizes of particles ranging from sand to stone. Ballast can have a varying proportion of sand/stone, so you may need to judge whether you need to add additional sand, if any.

Crushed stone is produced in quarries by crushing blasted rock and then the result is graded by being passed through a succession of sieves. In theory, this should make better concrete than rounded stone from gravel pits, because of the sharp angular edges.

Concrete Mixing Ratios

A general purpose mixture suitable for fixing posts, making concrete pads, door steps, bases for garden sheds, floors etc. is known as a C20 mix. Materials are mixed by volume not weight.

A C20 mix consists of:

  • 1 part cement
  • 2 parts sand
  • 4 parts stone

Alternatively a mix of sharp sand and stone, sometimes called ballast or mixed aggregate can be used, and this is mixed 6 to 1 with the cement.

A stronger, more hard wearing C30 mix, suitable for thinner and narrower concrete slabs, e.g. pavements, consists of:

  • 1 part cement
  • 2 parts sand
  • 3 parts stone

As in the case of the C20 mix, if you're using ballast (sand and stone), mix it 5 to 1 with the cement.

Ideally stone should be 15 to 20 mm in size (9/16 to 13/16 inches).
Sharp sand should be used, graded from 0 to 5mm. Don't use fine stuff which is really for mortar/plastering.

How Much Water For Making Concrete?

The max amount of water that should be added is 0.55 times the weight of cement. So for a 25 kg bag:

25 x 0.55 = 13.75 kg or 13.75 litres

This is approximately the volume of a 3 gallon (Imperial) bucket. Since the aggregate may be wet, this can mean that less water is actually needed, so these values are approximate.

The mix shouldn't be sloppy and should be able to self support itself without slumping. Concrete that is too dry is unworkable. Sloppy concrete due to excess water will be weak.

What Does C20 Mix Concrete Mean?

It means the concrete can withstand a compressive force (or more correctly pressure) of 20 newtons per square millimetre (20 MPa) without crushing. So in theory, for a 10 cm x 10 cm square (about 4 inches x 4 inches):

Area = 100mm x 100mm = 10,000 square millimetres

So total compressive force that the concrete can withstand without crushing is:

Force = pressure x area = 20 N/mm2 x 10,000 mm2 = 200,000 newtons.

A newton is equivalent to a weight of about 0.1 kg so:

200,000 newtons = 200,000 x 0.1 = 20,000 kg weight or 20 metric tonnes on a 10 cm by 10 cm square.

In reality a concrete slab would probably crack or sink with much less than this magnitude of load. This is because the underside of the slab would be spanning the individual stones of the sub base foundation and not supported underneath at every point over its full extent. These figures really refer to the compressive strength of a 150 mm concrete cube, cured for 28 days as measured on a test jig.

Tools and Equipment For Mixing Concrete

  1. Builders shovel. (The pointy type one)
  2. Ideally three, 3 gallon buckets. One for water, one for cement and one for sand/stone. If the sand or stone is wet and you use this bucket afterwards for measuring cement, it will stick to the sides and bottom.
  3. Polythene sheeting. A sheet of polythene helps to prevent mess and contamination of the concrete by pebbles, leaves, soil and other debris. It also makes it easier to scrape up all the leftovers with no wastage. I use 1200 gauge polythene (the heavy stuff used as a damp proof membrane under concrete) and this is widely available in hardware stores. You can of course mix concrete in a wheel barrow or bucket, but there's more room to mix on a sheet.
  4. Wheelbarrow or buckets. For transporting the concrete to its final destination. Alternatively you can mix in situ.

For laying concrete, you can use a garden rake or a 1 x 4 board nailed or screwed onto a length of 1 1/2 x 2 for spreading.

Do I Need to Wear Personal Protective Equipment (PPE) When Mixing Concrete?

  1. A dust mask will help to prevent the inhalation of fine cement dust while measuring out.
  2. Gloves to protect hands. Cement is somewhat caustic when dry, so if you have sensitive hands, these will give protection.
  3. Safety glasses stop cement dust or splashes of concrete from getting into your eyes
  4. Steel toe-capped boots. Optional. You may end up standing in or close to concrete while mixing/laying. Steel toe-caps protect your toes from dropped bricks, blocks or rocks. They normally also have a steel insole to protect feet from nails, glass or other objects that penetrate the outer sole.

Buying Cement

Cement is generally available in 25kg bags. In the US it is sold in 47 or 94 pound bags

Mixing Concrete: Sand, Cement, Gravel, and Water

When mixing by hand, it is essential to thoroughly mix the concrete to get consistency throughout the mixture.

If you need to mix a small amount, for instance half a bucket, place the stone and sand and finally the cement into the bucket. This needs to be thoroughly dry mixed with a garden or block layers trowel. Water is then added, say half a pint at a time and mixed throughout the bucket. More water can be added until the concrete is at the required consistency. If the mixture becomes too sloppy, add more cement. If you are filling a hole in the ground e.g. around a post, the mixture can be a bit more sloppy so that it flows easier.

Larger quantities of concrete can be mixed on a flat surface on the ground

You can measure the proportions of the mix by counting shovels. However I find it easier to use buckets. If you go for a C20 mix, a single mix using buckets ( which totals 7 buckets of material) is enough to produce a wheelbarrow of concrete.

So remember you need:

  • 1 bucket of cement
  • 2 buckets of sand
  • 4 buckets of stone
  1. If you're using polythene sheet, spread it on the ground and weigh it down with blocks/bricks or whatever at the edges in windy weather
  2. Place the stone onto the ground followed by the sand. Alternatively you may have gravel which is a composite mix of large and small stone and sand. If there isn't much sand in the gravel, you can add some more
  3. Place the cement evenly onto the top of the pile. If you have someone to help you mix, it will be easier. Start at the edge of the pile with the other person facing you. The aim is for both people to keep shovelling the pile to one side to create a new pile adjacent to the old pile. Repeat this three times so that's four mixes in total.
  4. Now it's time to add the water. Make a crater in the top of the pile about half its diameter so that it looks like a volcano. Again, it's important that the pile doesn't have slopes that are too steep so when you add the water it breaks through the crater and runs down the slope! Add half the water, the amount depends on the amount of dry mix you have created.
  5. Now with the shovel, go around the edges of the crater and keep sliding the mix into the center. Then use a chopping motion with the edge of the shovel to mix the water with the dry mixture. Continue to shovel the dry mixture from the edges of the pile towards the center. Eventually the mixture will become easier to control as the water becomes more distributed. Then keep sliding the shovel under the mixture and turn it over bit by bit and use a chopping motion with the edge of the shovel to thoroughly mix the concrete.
  6. Continue adding water until the concrete is of a consistency that doesn't slump and can support itself in a pile.

Don't forget to wash your shovel when finished before the concrete sets on it!

Should Concrete be Sloppy or Stiff?

Ideally concrete should be able to stand up in a pile on a shovel and not slump.

How to Mix Concrete

Steps 1 to 8

Step 1: Spread a Plastic Sheet on the Ground

Step 2: Measure Out the Materials

Step 3: Place the Stone and Sand on the Sheet

Step 4: Place the Cement on Top of the Sand and Stone

Step 5: Shovel to One Side From the Edge of the Pile and Repeat Three Times

Step 6: Make a Deep Crater and Add Water

Step 7: Fold the Mix in From the Sides

Step 8: Continue to Fold Inwards and "Chop" the Pile to Distribute Water Through the Mix

Laying Concrete

  • Use timber boards placed at strategic points to act as ramps and bridges so that you can get your wheelbarrow over uneven terrain and ground at different levels
  • Don't try to push a loaded wheelbarrow up a step, it's easier to pull it
  • Spread concrete with shovels and a rake after you tip it out of the barrow. You can also make up a makeshift rake using a long length of timber with a board nailed to the end
  • If you use a cement mixer, obviously you can empty the concrete directly at the point where you need it, rather than transferring to a wheelbarrow
  • When laying concrete floor sections adjacent to each other, feather the edge of the new concrete with a sweeping brush so that it blends with the previously laid section

Laying a Concrete Slab

  • If you're laying a concrete slab, tip the mix from the barrow within the formwork (the boards which bound the slab) and furthest from the front. Roughly scrape out the barrow and use a rake to spread the concrete, making sure its pushed into all corners. Use the back of the rake with the handle vertical to compact and pack the concrete, especially around the edges of the formwork.
  • Start a new mix
  • Continue to build up the level of concrete until it's about 1/2" above the formwork boards.
  • If you work fast and alone, you should be able to lay about 3 barrow loads of concrete before a slab needs to be screeded (roughly levelled flush with the forms with a timber board)

Curing of Concrete

During curing or hardening of concrete, a process called hydration occurs where water chemically bonds to cement. So some of the water you added actually never dries out. It is locked to the cement in a bond forever!

Protecting Concrete in Cold Weather (or Dry Weather)

The best time to make concrete is when the weather is mild. Freezing weather conditions can weaken concrete and hot dry weather can cause water to evaporate too quickly so that there is insufficient water for it to cure properly, resulting in cracking.

Until concrete cures, it should be protected from the weather and never allowed to freeze for the first 24 hours. Minimum curing temperature should be 40 F (4C). In freezing weather conditions, water in concrete expands as it freezes. As ice crystals grow, they push the concrete outwards, breaking bonds between cement, stone and sand. Then when they melt, they leave millions of micro-cavities, so the concrete ends up porous like a sponge, potentially weakening it.
You can cover concrete slabs after laying with blankets/polystyrene/bubble wrap or whatever to help prevent it freezing. If frost is due to set in at night, lay your concrete early in the day so that it firms up, before covering with insulating material (otherwise it'll get marked by the covering).

In hot, dry weather, wait for a few hours until the concrete firms up. Then cover it with polythene to prevent moisture loss and cracking.

How to Make Concrete Stronger

Concrete is only strong in compression, not tension. This means that it'll withstand being squeezed but not bent. So for instance a concrete pillar in a building can withstand tons of weight pushing down on it, but a concrete beam spanning an opening (e.g. a large doorway in a building) would snap under moderate load. To strenghten it, steel bars called reinforcing bar or rebar is inserted when the concrete is wet. Because steel is strong under tension, the resulting composite material becomes strong both under compression and tension.
You can add rebar rods or grid to concrete when laying floor, pads or anywhere you think that it'll be subject to heavy loads and in danger of cracking. It's also a great way of getting rid of any scrap iron you've accumulated.

Does Cement Have a "Best Before Date" and How Do I Store It?

Use cement within 3 months of the date of manufacture on the bag. Store it off the ground to prevent moisture soaking into the bags and making it lumpy.

How to Mix Concrete With a Cement Mixer

If you decide to use a cement mixer, checkout my other guide, "Easy Steps to Mixing Concrete With a Cement Mixer"

Questions & Answers

Question: What volume of concrete would your 7 bucket mix make?

Answer: About a wheelbarrow. Buckets are 3 imperial gallons or 3 x 4.54 liters. From a quick Google search, a builder's wheelbarrow is 65 to 85 liters in volume.

Question: What is curing?

Answer: It's a chemical reaction in the concrete during which water bonds with calcium compounds. During the curing process, excess water also evaporates and the concrete becomes stronger.

Question: How long does it take concrete to cure?

Answer: Under normal drying conditions, you can usually walk on concrete after 24 hours. A general rule is that it reaches 70% strength after a week and a month to get near full strength. Concrete will continue to strengthen however over months and years. Its best to avoid putting heavy items on it for a week and don't drag things across it which can leave scrape marks.

© 2012 Eugene Brennan

Jacob Shuma on March 13, 2019:

Question:

How do I hand mix concrete for feature beam with normal materials e.g cement, stones and crusher sand?

VCA Mobile Concrete on March 06, 2018:

Great! Thank you for the sharing us this knowledge, How to Mixing Concrete by Hand.

Rick on April 18, 2017:

In Peru, we use three(3) small wheelbarrows (about 20 full shovels per wheelbarrow) of sand/rock mix (called 'ripio') to one 42.5kg sack of Andino Type I cement. I've seen it mixed as light as seven(7) wheelbarrows/sack but, I don't know that I would trust that ratio.


Watch the video: How much Cement,Sand u0026 Aggregate is required for M20 Grade Concrete? (May 2021).